The invention concerns a process for controlling a continuously variable transmission (CVT) installed in the power train of a motor vehicle between a drive engine and a drive axle.
In a CVT, i.e. a continuously variable automatic transmission, depending on the driver""s desire regarding the vehicle""s operating behavior, a consumption-optimized or driving performance-optimized control curve in an engine characteristic field is selected by means of a selector switch or automatically. In this context, however, the disadvantage arises that as a result of the typical adjustment characteristic of the CVT, i.e. the constant engine rpm during acceleration, the driving behavior is perceived by the driver as not corresponding to his wishes especially as a result of the acoustic feedback. The fixed control of the CVT may also fail to take into account the varying factors and driving conditions such as slopes, gradients, head wind, a pulled load, etc.
In order to counteract this shortcoming, DE 197 42 604 A1 proposes that preferably the nominal rpm of the drive engine be determined as a response to a change in the position of the accelerator pedal as a function of a responder function with a jump component, in which case the responder function varies over a time which passes since the change in the position of the accelerator pedal.
In this way, during an acceleration process, an acoustic feedback acceptable for the driver can indeed be achieved. However, the operating behavior of the CVT in the case of constant operation of the vehicle is not improved by such a measure, e.g., in the case of driving at a constant speed but during which unevennesses on the road, the effects of wind, variable rolling resistance or similar disturbing factors arise which the driver compensates for or attempts to compensate for by scarcely perceptible and often unconsciously performed changes in the position of the accelerator pedal.
As a result of such disturbing factors, and also due to the resulting usually only slight changes in the position of the accelerator pedal, the CVT reacts by changes in the transmission ratio in order to remain on the preassigned control curve. This results in an unstable driving state in which the engine rpm varies around a mean value while simultaneously the CVT compensates for these fluctuations by changing the transmission ratio. For the driver this state generally causes disturbing sensations.
The invention has the objective of improving the process for controlling a CVT installed in the drive train of a motor vehicle in such a way that in the case of a constant driving state of the motor vehicle any of the above, described inconveniences which occur are eliminated.
The invention solves this problem by characterized by the following steps:
in the case of a change in the accelerator pedal position it checks whether this change is within a value (a) relevant for the driving behavior or lies above it, in which case only when the values is above it does it intervene in the usual manner in the regulation of the transmission ratio of the CVT in the form of a change in transmission ratio;
if it is found that the change in the accelerator pedal position is below a value (a) relevant for the driving dynamic, it checks whether the driving speed (S) has changed to above a calibrated range around the current driving speed or remains within this calibrated range (S1 less than S less than S2) in which case only upon the recognition of a change in driving speed outside of the calibrated range (S1 less than S less than S2) does it intervene immediately and in the usual way in the regulation of the transmission ratio in the form of a change in the transmission ratio of the CVT;
if it is found that the change in the driving speed remains within the calibrated range (S1 less than S less than S2) it does not intervene in the regulation of the CVT in the form of a transmission ratio change, and the existing transmission ratio remains constant.
Advantages modifications of the invention of the invention are characterized by the fact that the calibrated range (S1 less than S less than S2) varies in magnitude as a function of the actual driving speed (S) and by the fact that the calibrated range (S1 less than S less than S2) becomes greater with increasing driving speed (S).